Stabilized distillate fuels



3,080,223 Patented Mar. 5, 1963 3,080,223 STABILIZED DISTILLATE FUELSPhilip Monuikeudam, Nanuet, N.Y., John V. Clarke, Jr.,

Cranford, NJ., and James P. Black, Brooklyn, N.Y., assignors to EssoResearch and Engineering Company, a corporation of Delaware No Drawing.Filed June 29, 1960, Ser. No. 39,451 16 Claims. (Cl. 44-73) The presentinvention relates to petroleum distillate fuels and more particularlyrelates to kerosines and aviation turbo fuels meeting the distillationspecification of ASTM specifications for Aviation Turbine Fuels,D-165559T, having incorporated therein minor amounts of a combination ofadditive agents which are effective for improving the stability andallied properties of such fuels. In a preferred embodiment, theinvention relates to fuels for turbo-jet aircraft, which fuels have beeninhibited against the formation of sludge, sediment and heat exchangertube deposits by a novel method and combination of additives free of thewater tolerance difficulties and other undesirable properties which havecharacterized additives suggested for this use in the past.

Gas turbine engines used in jet aircraft are provided with heatexchangers through which the engine lubricating oil is circulated inorder to cool the oil and prevent its thermal degradation. The fuelburned in the engine is used as the cooling medium or a heat sink inthese heat exchangers. As the fuel passes through the heat ex" changer,it undergoes a temperature increase of several hundred degrees in amatter of seconds. Any unstable constituents in the fuel quickly reactunder these severe conditions to form deposits which adhere to the heatexchanger tube surfaces and the nozzles through which the fuel issubsequently sprayed into the engine combustion chamber. The heattransfer characteristics of the heat exchangers are impaired by thepresence of these deposits. Deposits formed on the insides of thenozzles cause distortions in the fuel spray pattern which may result inuneven heating and eventual warpage of the combustion chamber liners ofthe engine. It is expected that turbine powered aircraft will beoperating at ever increasing speeds and temperatures, thus thetemperature to which the fuel can be brought without undergoing thermaldegradation is becoming of extreme importance. Presently used turbofuels are thermally stable at the 300 F. temperature level, but begin todegrade before the temperature reaches 400 F. Future fuels will berequired to maintain their thermal stability at tempera tures of from450 to 600 F.

Certain dispersant ashless additives have been proposed in the past toprevent the accumulation of deposits, but the use of such additives hasnot been successful. The problems caused by the tendency ofdispersant-type additives to suspend water with which aviation turbofuels come into contact are equally serious. At the temperaturesprevailing at the altitudes at which jet aircraft must operate to obtainmaximum fuel utilization, any water dispersed in the fuel quicklyfreezes to form ice crystals which may block screens, lines, andorifices in the distribution system through which the fuel istransferred from one fuel tank to another, and from the fuel tanks intothe engine itself. Since jet fuels are frequently stored and transportedin tanks containing an aqueous phase, the use of dispersant additiveswhich promote the suspension of water increases the likelihood thatwater will be present in the fuel as it is introduced into the aircraft,and hence increases the danger that ice formation and accompanyingdifficulties will occur.

These and other difticulties encountered with additives employed in thepast for improving the stability of aviation turbo fuels are avoided inaccordance with the present invention through the use in such fuels of acombination additive agent which is considerably more effective forpreventing the formation of sludge, sediment and deposits than aredispersants in general. This additive combination at the same timeexhibits little or none of the tendency toward the suspension of waterwhich has characterized dispersant-type additives used heretofore. Ithas now been found that the use of certain phosphosulfurizedhydrocarbons having molecular weights between about and about 50,000 incombination with certain metal chelating agents as additives fordistillate fuels results in fuel products which are surprisingly stableunder extremely severe conditions and which have excellent watertolerance properties. Moreover, the additive combinntion of theinvention is effective at very low concentrations, is substantiallyashless, is compatible with a wide variety of other additives, and hasother characteristics which render it particularly attractive for use asan additive agent in distillate fuels. In addition, it has beendiscovered that certain processing of the turbo fuel with the subsequentincorporation of the additive combination of the invention results in afuel product of exceptionally high thermal stability.

The phosphosulfurized hydrocarbons which are utilized as one constituentof the additive combination of the invention are prepared by reacting aC to C olefin polymer with a sulfide of phosphorus. Olefinic polymersprepared by the polymerization or copolymerization of low molecularweight olefins and diolefins such as ethylene, propylene, butylene,isobutylene, butadiene, isoprene, and cyclopentadiene, are suitablematerials for the phosphosulfurization. Polymers of mono-olefins whereinthe molecular weight ranges from about 100 to about 50,000 andpreferably ranges from about 250 to about 10,000 are particularlyeffective in preparing the phosphosulfurized hydrocarbons of theinvention.

One method of carrying out such a polymerization reaction is to employ aFriedel-Crafts catalyst such as boron fluoride or aluminum trichlorideat low temperatures in the range of from about 0 F. to about 40 F. Othermethods familiar to those skilled in the art, carried out at highertemperatures and with other polymerization catalysts may also be used.Polypropylenes and polyisobutylencs having average molecular weightsbetween about 300 and about 8000 are particularly effective. v

The sulfide of phosphorus employed in preparing the phosphosulfurizedhydrocarbons may be P 8 P 8 P 5 P 8 or a similar phosphorus sulfide. asa phosphosulfurizing agent.

The phosphosulfurization reaction may be effected by reacting 2 to about5 moles of the olefin polymer with each mole of the phosphorus sulfideat temperatures of from 200 to 600" F. It is usually preferred to addthe phosphorus sulfide to the oil in powdered form at a temperature inthe range of from about 200 F. to about 250 F. and then to heat themixture to a reaction temperature between about 300 F. and about 400 F.Agitation should be provided during the addition of the phosphorussulfide in order to ensure complete mixing. The mixture is held at thereaction temperature for a period of from about 2 to about hours and atthe end of that time is filtered to obtain the phosphosulfurizedhydrocarbon product. It is ordinarily desirable to employ an amount ofthe phosphorus sulfide that will react completely with the olefinpolymer. The reaction is continued until substantially all of thephosphorus sulfide has been reacted. In some cases it may be founddesirable to blow the product with steam, alcohol, ammonia, or an amineat an elevated tem perature in the range of from about 200 F. to about300" F. in order to improve the odor of the product.

The second constituent of the additive combination of the invention maybe a variety of metal chelating or metal deactivating agents. Preferredchelating agents are those prepared by the condensation of a hydroxyaromatic aldehyde such as salicylaldehyde with an alkylene polyarnine.The preferred class of metal chelating agents are thoseN,N-disalicylidene-di-amino-alkanes, wherein the alkane group has from 1to 6 carbon atoms, i.e. can be ethane, propane, butane, pentane, andhexane, and the amino groups are on the carbon atoms separated by nomore than one carbon atom. A particularly desirable member of this classis N,N-disalicylidene 1,2-propanediamine. This material is preferablyadded dissolved in a vehicle such as xylene. Other chelating agentssimilarly effective include the condensation products of sallcylaldehydewith amino phenols, the tetraammonium salt of ethylene diaminetetraacetic acid and N,N'-bis(acetylacetone) ethylene diamine.

The phosphosulfurized polymers are employed in the distillate fuels ofthe invention in concentrations ranging from about 1 to about 30 partsper million, based on the weight of the fuel. Concentrations betweenabout 2 and about 10 parts per million have been found to be effectiveunder extremely severe conditions and will be preferred in most cases.The metal chelating agents employed as the second constituent of theadditive combination are used in concentrations ranging between about 5and about 60 parts per million, again based on the weight of the fuel.Metal chclating agent concentrations ranging between about 10 and about30 parts per million are preferred. The total amount of the combinedadditive agent employed may thus range from about 6 parts per million toabout 90 parts per million and will preferably fall between about 12parts per million and about 40 parts per million. It is generallydesirable to utilize the metal chelating agents in concentrations offrom 1 to 25 times the concentrations in which the phosphosulfurizedpolymers are used, with from 3 to 12 times the preferred concentrationrange.

The fuels in which the additive combination of the invention is used arepetroleum distillate fuels meeting the P 8 is preferred ASTMdistillation specifications for Aviation Turbine Fuels, Dl655-59T, andwhich preferably boil in the range between 300 F. and about 550 F. Thesedistillate fuel products frequently exhibit unstable characteristicswhich can be overcome or greatly reduced by means of the additivecombination. As pointed out heretofore, the combined additive agents areparticularly beneficial when used in aviation turbo fuels, and permitthe marketing of such fuels with significantly higher stability levelsthan can be obtained with equivalent amounts of additives employedheretofore. Specifications for aviation turbo fuels are set forth inU.S. military specifications MIL-F- 4 MIL-F-5624D, MIL-F-25558B(1), andMlL-F-25656(l) and in ASTM specifications for Aviation Turbine Fuels,D-l655-59T. The properties of such petroleum distillate fuels are wellknown to those skilled in the art and need not be set forth in detail topermit an understanding of the present invention.

The additive agents which make up the combination additive employed forimproving distillate fuel stability in accordance with the invention maybe added directly to such fuels or may instead be blended in a diluentto form a concentrate which is subsequently added to the fuels. Anorganic solvent such as benzene, xylene, toluene, diethylene glycol,pyridine, kerosene, or the like may be used as the vehicle for such aconcentrate.

The nature and objects of the invention may be more fully understood byreferring to a series of tests carried out to determine the effect ofthe additive combination when used in petroleum distillate fuels.

In a first series of experiments, various amounts of phosphosulfurizedpolyisobutylene and disalicylal diami nopropane were added individuallyand in combination to a number of aviation turbo fuels and keroseneswhich were then tested to determine their thermal stability by means ofCFR fuel coker tests. The base fuels employed in this first series ofexperiments had the following prop erties:

Property Base Base Base Base Base fuel 1 fuel 2 fuel 3 fuel 4 fuel 5Gravity. API 41. 0 44. 6 43. 3 42. 5 40. 2 Free-tine point, l -00 -43 60-59 -70 AS 1 M distillation:

Initial boilin': point." F 359 324 323 334 371 10% point. F 407 354 374361 298 50% Point. F" 4H 419 410 399 436 point, F- 406 495 489 469 489Final tnilinz point, F 530 544 535 494 52-1 Smore point, mm 23. 0 25. 024. 0 20.0 24. 0 Sulfur. wel ht. percent 0. 02 0.077 0.076 0.017 0. 027Heat content. B.t.u/# 18,685 18, 720 18, 705 18, 501 18, 694

The CFR fuel coker test used to measure the thermal stability of samplesof the above fuels with and without the additive combination is carriedout in apparatus which closely resembles an actual fueling system. Thefuel is pumped from a supply tank through a screen and rotam eter to anannular aluminum heat exchanger where it is heated to the testtemperature. The heated fuel is then passed from the heat exchangerthrough a sintered metal filter held at a temperature F. above the fueltemperature. Fuel performance is determined by measuring the timerequired for the pressure drop across the metal filter to increase by 25inches of mercury or by the pressure increase which occurs during 300minutes, whichever takes place first. This test has been found to givean extremely reliable indication of the stability properties of a turbofuel under actual service conditions. The test is more fully describedin CRC Manual No. 3, dated March 1957, of the Coordinating ResearchCouncil of the American Petroleum Institute and the Society ofAutomotive Engineers.

Due to recent increases in the stability level required of aviationturbo fuels, CRC fuel coker tests of such fuels carried out at preheatertemperatures of 400 F. and filter temperatures of 500 F. are generallyconsidered a better indication of the acceptability of a fuel from thestability standpoint than are tests carried out at the 300 F./400 F.level. In order to demonstrate the surprising eifectiveness of theaddition of the invention, samples of the fuels described abovecontaining a number of commercial additive agents which have resulted infuels of acceptable stability at the lower test conditions were testedat the 400/500 F. level along with the additive of the invention. Theresults of these tests are set forth in Table I below.

Additive CFR fuel coker Base I concentratest results 1 fuel Additive 1tion. by No. weight.

parts per Merit Tube dcznillion rating posits 3 None None 110 4 AdditiveA.. 6. 7 900 4 Additive A.. 3. 3 830 2 Additive B. 13.3 None None 270Additive A 3.3 900 1 Additive 13.. 13. 3 None None 310 2 Additive A 3.3000 1 Additive B 13.3

one None 180 4 Additive B 50 115 Additive 0.. 6. 7 630 4 Additive C 13.3825 4 Additive B 9.3 900 1 Additive C 6. 7 Commercial a 150 200 3Commercial additive E. 70 820 4 Commercial additive F 56 850 4Commercial additive G. 70 410 4 Commercial additive II 70 298 4Commercial additive I 7 375 4 The additives tested were the following:Additive A- Polyisobutylene having about 1,100 average molecular weight,treated with 15 weight percent Pass. Additive B-Disalicylaldiaminopropaue. Additive CPolyisobutylene having about 1,100 averagemolecular weight. treated with 10 weight percent P285. Commercialadditive D-4,4'-bis(2-methyl-6-tertiaryoutylphenol). Commercial additiveE-An alkylcoco amine phosphate. Commercial additive F-A dimer oflinoleic acid with a minor amount of an alkyl phosphate. Commercialadditive G-Etl1vlene diamiue salt of dinonyl naphthalene sulfonic acid.Commercial additive II-NH4 salt of dinonyl naphthalene sulfonic acid.Commercial additive I- Amine salt of dilinoleic acid.

-Tests with base fuels 1, 2, and 3 were carried out with 300 F.preheater temperature and 400 F. filter temperature. Tests with basefuel 4 were carried out with 400 F preheater temperature and 500 F.filter temperature.

".lube deposits were rated as follows: No visible deposits. lvisiblehaze or dullmg but no visible color. 2- Barely visible dlscloroation.3Light tan to peacock stain. 4-1-Ieavier than 3.

Norm-A rating of 2 is considered the maximum acceptable rating.

The data in the above table demonstrate that a combination of as littleas 3.3 parts per million of phospho snlfurized polyisobutylene and 13.3parts per million of disalicylal diaminopropanc resulted in a fuelhaving excellent stability characteristics from the standpoint of bothmerit rating and tube deposits. The merit rating is primarily anindication of the tendency of the fuel to clog screens, orifices andfilters in a fuel system; while the tube deposit rating measures theextent to which deposits will be built up in the heat exchanger tubesand nozzles of a turbine engine operated on the fuel. The data in thetable show that neither the individual constituents of the additivecombination of the invention nor a large number of commercial additiveswere as effective as was the combination. The commercial additivestested were all additives which have been proposed to give acceptablestability when tested at the 300/400 F. level. The data show that noneof these commercial additives raised the stability of any of the fuelssufiiciently to meet the requirements of the more severe 400/500 F.test, despite the fact that they were used in concentrationsconsiderably higher than the concentrations at which the additivecombination of the invention was found effective.

Further tests carried out to determine the effect of the additivecombination upon the Water tolerance of fuels to which it is addeddemonstrated that the additive combination is free of the adverse effectupon water tolerance which has characterized additives employedheretofore. The tests employed were carried out in accordance with themethod described in Federal T est Standard No. 791, Method 3251.6,Interaction of Water and Aircraft Fuel." In brief, this test involvesthe agitation of 80 cc. of the fuel to be tested with 20 cc. of waterfor a two-minute period, after which the mixture is allowed to I settlefor five minutes. At the end of the settling period, the condition ofthe fuel-water interface is noted. The interface is assigned a rating asfollows.

INTERACTION OF WATER AND AIRCRAFT FUELS [Method 3251.6, Fed. Test Std.N0. 791] Appearance of interface: Interface rating Clear and clean 1 Afew small clear bubbles covering not more than 50% of the interface 1BShred of lace and/0r film at interface 2 Loose lace and/or slight scum 3Tight lace and/or heavy scum 4 TABLE 'II Effect of Additives UponFuel-Water T olerance Additive concentration Water Base fuel No.Additive by wcivht, tolerance parts per interface million rating 1 NoneNone 1 Additive A" 6. 7 2 Additive 13.- 3.3 1B Additive B" 13. 3

None 1 8. 3 1B 13.3 None 1 3. 3 1B Additive 13.. 13.3

The data set forth in Table II above demonstrate that the use of theadditive combination of the invention in aviation turbo-jet fuels andsimilar distillate fuel products does not increase the interface dcmcritrating above the acceptable level of 1B. The additives, unlikedispersant-type additives employed to improve the stability of turbo-jetfuels and similar products in the past, meet the critical watertolerance requirements for such fuels and do not materially increase thedanger that appreciable amounts of water will be suspended upon contactof the fuels with the aqueous phase present in storage tanks, pipe linesand tank trucks. This improved water tolerance constitutes an extremelyimportant advantage of the additive combination of the invention overstabilizing additives used in the past.

While water tolerance tests of the type described above have been widelyused, they have not always been satisfactory in predicting fieldperformance. More recently, the effect of fuel additives on the watertolerance of fuels has been investigated by a method that gives greatlyimproved correlation with field performance. This new method uses asmall filter-separator similar to the larger filter-separator units usedon aircraft rcfuelcrs. In the particular test here described, 1% ofwater was added to the fuel ahead of a gear pump, which provides themixed fuel-water input to the filter-separator. The effluent from thefilter-separator was examined for Water content both analytically andvisually. In the following table, the additive combination of theinvention is compared with the base fuel and with two corrosioninhibitors approved under military specification MIL-F-5624D.

7 TABLE III Eflect of Jet Fuel Additives n Water-Carryover ThroughLaborat ry Filter-Separator 1 1% water added to fuel ahead of rear pump.

2 ASTM Turbine Fuel Type C (ASTM Standards on Petroleum Products, 1958).

3 As in Table I.

This table shows that the additive combination of the invention hasessentially no effect on water carryover even when used inconcentrations well above those required for good fuel stability. Inthis respect, the additive combination of the invention is far superiorto commercial additives previously approved for use in jet fuel.

An exceptionally thermally stable turbo fuel composition which willsuccessfully pass the critical fuel coker test at 450/500 F. can beobtained by the process of alkali or caustic washing, followed by waterwashing the petroleum fuel prior to the incorporation of the additivecombination of the invention. The caustic washing is accomplished in theconventional refinery manner by scrubbing the fuel mixture with anaqueous solution of a strong base such as sodium hydroxide, caustic sodaand the like. A strong caustic solution concentration of at least 5 Baumwith a caustic solution to fuel ratio of from 1/20 gallons to l ispreferred. The caustic wash is followed by an aqueous wash in theconventional refinery manner to remove any entrained caustic or otherimpurities, such as amines and the like, utilized in the various causticregenerative processes. Water washing can be carried out in amixer-settler or in a tower if more intimate contact is desired.

The results achieved by this process and the inventive additivecombination in producing a highly stable turbo 4 fuel is more fullyshown by Table IV.

TABLE IV Eflect of Caustic and Water Washing and Additives on Stabilityof Jet Fuel CFR fuel eokcr test results, 450/500 F. Base Causticiuelwater Additive 5 5 No. treatppm. Code Filter Pressure ment 1 rating testdrop across tube time in filtcr,in. deposits minutes of lig 5 (1)....None None 4 133 25 s (2)-- ---do---.- Additive 1L3..- 4 300 0 AdditiveB. 50-- 5 (3)-.. Yes".-- None 4 225 25 5 (4)... Yes... Additive A. 3...2 300 0 Additive B. 50..

'lreatment of fuel consisted of caustic washing with agitation in astainless steel vessel with a 30 Be. sodium hydroxide solution and aeaus tic solution incl ratio of gallons for one hour followed by twofiveminute water washes.

2 See footnote 1 of Table I for additive identification.

3 Tests conducted in standard CFR fuel coker with 450/500 F.preheater/filter temperature at fuel flow rate of 6 lbs./hr.. and 5hours operatice time. All data was result of duplicate tests except foritem 1.

1 Tube deposits were rated as in Table I. footnote 3.

drop of 12 inches of mercury in 300 minutes, and a maximum preheatertube deposite code rating of less than 3. As shown, the caustic-waterwash alone did not change the tube deposit rating of the base fuel andgave only slight improvement in the time to reach a filter drop pressureof 25" of mercury. The separate incorporation of the additivecombination of the invention to the base fuel did improve both the tubedeposit rating and the filter drop pressure and time, but notsufficiently to allow it to pass the more severe specifications at a450/500 F. preheater/ filter test level. The combination of thecausticwater wash with the subsequent addition of the additivecombination gave the unexpected result of increasing the thermalstability of the fuel beyond the expected levels when either componentwas used independently. The surprising improvement in thermal stabilitywhich allows the fuel to meet the high specifications recited allows theuse of these fuels at a much higher temperature range without danger ofexcessive deposit formation and filter plugging.

As demonstrated, a caustic treatment with water washing followed by theaddition of the inventive combination imparts exceptional thermalstability to a previously unstable turbo fuel. The data of Table V asfollows establishes that caustic concentrations of 5 Baum and above areeffective for this purpose, with a Baum concentration of 5 to 50especially preferred. Suitable caustic solutions are those of sodium,magnesium, potassium hydroxide, and the like. The methods of caustictreating and water washing hydrocarbons, particularly petroleum fuels,are well known, and are set forth, for example, in Petroleum RefineryEngineering by W. L. Nelson; Mc- Graw-Hill Book Company, Inc., 1941;Chemical Refining of Petroleum by V. A. Kalichevsky and B. A. Stagner,Reinhold Publishing Corp., 1942; and other publications.

TABLE V Eflect of Caustic Concentration on Stability of Jet Fuel CFRfuel coker test results, I Caustic 450/500 F. Base concentra- Additive,

fuel tion in p.p.m. N 0. Baum Code Filter test Pressure Rating time indrop across tube deminutes filter. in. of

posits 4 Hg 1 Treatment of fuel as in footnote 1 of Table IV, except forusing caustic concentration.

2 Additive concentration 3 p.p.m. additive A with 50 p.p.m. additive 5As in Table IV, footnote 3. As in Table IV, footnote 4.

What is claimed is:

1. A petroleum distillate fuel meeting the ASTM distillationspecifications for Aviation Turbine Fuels, D- 1655-59T, and havingimproved water tolerance and thermal stability characteristics to whichhas been added from 6 to about parts per million of a thermal stabilityadditive consisting essentially of: (l) a phosphosulfurizedhydrocarbonobtained by reacting about 2 to about 5 moles of a C to C olefin polymerof from to about 50,000 average molecular weight with about 1 mole of asulfide of phosphorus at a temperature of from 200 to 600 F. and (2) aN,N-disa1icylidene-diaminoalkane chelating agent wherein the alkanegroup has from 1 to 6 carbon atoms, said chelating agent being presentin a concentration ratio of from 1 to 25 times the concentration of saidphosphosulfurized hydrocarbon.

2. A fuel as defined by claim I wherein said concentration ratio is from3 to 12.

3. A fuel as defined by claim 1 wherein the said olefin polymer has anaverage molecular weight of from 250 to about 10,000.

4. A fuel as defined by claim 1 wherein said chelating agent is1,2propaue diamine-N,N-disalicylidene.

5. A fuel as defined by claim l wherein the said additive has been addedfrom 1?. to 40 parts per million.

6. A fuel as defined in claim 1 wherein said fuel is a caustic-aqueouswashed turbo-jet fuel.

7. A petroleum turbo-jet fuel boiling in the range between 300 and about550 F. and having improved water tolerance and thermal stabilitycharacteristics, to which has been added from 12 to 40 parts per millionof a thermal stability additive consisting essentially of: (l) aphosphosulfurizcd hydrocarbon obtained by reacting about 2 to about 5moles of a C to C olefin polymer of from lit to about 10.000 averagemolecular Weight with about 1 mole of a sulfide of phosphorus at atemperature of from 200 to 600 F. and (2) a chelating agent ofSEN-disalicylidene-diamiuo-alkane, wherein the alkane groups have from 1to 6 carbon atoms, said chelating agent being present in a concentrationratio of from 3 to 12 times the concentration of the saidphosphosulfurized hydrocarbon.

s. A fuel as defined in claim 7 wherein said olefin polymer ispoiyisobutylenepf about 1100 average molecular weight.

9. A fuel as defined in claim 7 wherein said N,N'-salicylidenediai'nino-all;ane is 1,2 propane diatnine N,N'-disalicylidene.

10. A process for cooling the lubricating oil in a jet engine comprisingusing as a coolant for heat transfer with the lubricating oil athermally stabilized petroleum distillate fuel boiling in the rangebetween 300 to 550 F., to which has been added from 6 to about 90 partsper million of a thermal stability additive consisting essentially of:(1) a phosphosulfurized hydrocarbon obtained by reacting about 2 toabout 5 moles of a C to C olefin polymer of from 100 to about 50,000average molecular weight with about 1 mole of a sulfide of phosphorus ata temperature of from 200 to 600 F. and (2) a chelating agent of aN,N-disalicylidene-diamino-alkane wherein the alkane group has from 1 to6 carbon atoms, said chelating agent being present in a concentrationratio of from 1 to times the concentration of said phosphosulturizedhydrocarbon.

11. A process as defined in claim 10 wherein said concentration ratio isfrom 3 to 12.

12. A process as defined by claim 10 wherein the said olefin polymer hasan average molecular weight of from 250 to about 10,000.

13. A process as defined by claim 10 wherein said chelating agent is-a1,2-propane diamine-N,N'-disalicylidene.

14. A process as defined by claim 10 wherein the said additive has beenadded from 12 to 40 parts per million.

15. A process as defined in claim 10 wherein said fuel is acaustic-aqueous washed turbo-jet fuel.

16. A process as defined in claim 10 wherein said fuel has been causticwashed with a 5 to Baum solution of sodium hydroxide at a caustic tofuel ratio of from 1/20 to l/l.

References Cited in the file of this patent UNITED STATES PATENTS2,316,078 Loane et al. Apr. 6, 1943 2,316,080 Loane et al. Apr, 6, 19432,382,905 Pedersen et al. Aug. 14, 1945 2,626,208 Brown Jan. 20, 19532,768,999 Hill Oct. 30, 1956 2,932,942 Ecke et a1 Apr. 19, 19603,0l4,793 Weisgerber et al Dec. 26, 1961

1. A PETROLEUM DISTILLATE FUEL MEETING THE ASTM DISTILLATIONSPECIFICAIONS FOR AVIATION TRUBINE FUELS, D1655-59T, AND HAVING IMPROVEDWATER TOLERANCE AND THERMAL STABILITY CHARACTERISTICS TO WHICH HAS BEENADDED FROM 6 TO ABOUT 90 PARTS PER MILLION OF A THERMAL STABILITYADDITIVE CONSISTING ESSENTIALLY OF: (1) A PHOSPHOSULFURIZED HYDROCARBONOBTAINED BY REATING ABOUT 2 TO ABOUT 5 MOLES OF A C2 TO C4 OLEFINPOLYMER OF FROM 100 TO ABOUT 50, 000 AVERAGE MOLECULAR WEIGHT WITH ABOUT1 MOLE OF A SULFIDE OF PHOSPHORUS AT A TEMPERATURE OF FROM 200 TO 600*F. A AND (2) A N, N-DISALICYLIDENE-DIAMINOALKANE CHEALTING AGENT WHEREINTHE ALKLANE GROUP HAS FROM 1 TO 6 CARBON ATOMS, SAID CHEALTING AGENTBEING PRESENT IN A CONCENTRATION RATIO OF FROM 1 TO 25 TIMES THECONCENTRATION OF SAID PHOSPHOSULFURIZED HYDROCARBON.